This is legally required today. It's not necessarily a reflection of Waymo. Whether their system was perfect or not, it's legally required they do this till the government changes their minds.
California DMV regulations do allow testing of autonomous vehicles without a safety test driver if certain conditions are met, spelled out in Title 13, Division 1, Chapter 1 Article 3.7 Section 227.38 [1]. The most technically challenging of these is that the car must be capable of operating at SAE level 4, which goes back to the OP's comment. CUPC licensing for commercial passenger services also allows this [2].
That said, I agree with others that this is the natural progression of testing rollout and doesn't tell us anything about the pace at which the rollout will occur, in particular whether it will be faster or slower than Phoenix.
Yeah, the commenter straight up assumes that a person is present because the L4 tech doesn't work, when in reality there are legal, liability, and even user comfort reasons to have someone on board with this new pilot.
